This invention relates to a family of ferrocene ionic charge complexes having utility as filtering materials suitable for use as a filtering component in an optical filter.
Optical filters are well known and widely used devices for passing radiation of selected wavelengths and simultaneously rejecting undesirable wavelengths. One of the most commonly used types of optical filters in the photographic and xerographic mode is the band-pass filter. Generally speaking, such filters comprise alternating layers of a dielectric material having a relatively high index of refraction and a dielectric material having a relatively low index of refraction. By making the layers of the proper thickness, the reflections of certain bands of wavelengths from the boundary between the materials are reenforced and thereby removed from the transmitted beam. The remaining wavelengths, which are grouped together in a plurality of orders having widely spaced bands, pass through the material. Such interference filters generally tend to be expensive because of the problems inherent in their manufacture. Expense notwithstanding, however, the rapid development both in photographic, electrophotographic, and xerographic technology in the area of multicolored records has accented the basic need for new and better filtering means in order to achieve the proper color balance and sensitivity at a price acceptable in the market place.
Generally, a complex formed between an electron donor and an electron acceptor retains the absorptions of the components modified to some extent, together with one or more absorption bands characteristic of the complex as a whole. The extra absorptions characteristic of the complex is readily observed in the interaction is between a strong donor and a strong acceptor. In such cases, the transition appears as a separate band at considerably longer wavelengths than the absorptions of the component molecules. The intensity of the absorption band of a complex is usually determined as the molar extinction coefficient at the wavelength of maximum absorption. However, a direct determination of intensity cannot always be made, due to the high degree of dissociation of the complex in solution.
It is an object of the present invention to obtain a new class of ionic charge transfer complexes which can be readily produced and which can be incorporated into existing photographic and xerographic systems for use as light filtering material.
It is a still further object of the present invention to obtain suitable filtering material which is stable under normal photographic and xerographic conditions and which will efficiently and precisely absorb light within the 3500- 6000 Angstrom range.